The present invention relates generally to vibrating screeds and strike-offs for finishing plastic concrete. More particularly, the present invention is directed to a floating, vibrational screed adapted to finish plastic concrete without forms. The invention is believed best classified in U.S. Class 404, subclasses 114 and/or 118.
As will be recognized by those skilled in the concrete placing and finishing arts, after concrete is initially laid during construction, the upper surface must be appropriately finished to give it a smooth, homogenous and correctly textured form and appearance. A wide variety of vibrating equipment such as screeds for treating plastic concrete have previously been suggested. Known prior art systems include "bull" floaters, various forms of finishing boards, strike-offs, and the like. The "strike-off" phenomena involves contact of rough unfinished plastic concrete with a leading, cutting, or blade-like edge to initially form and grade fresh concrete.
It is conventional to employ vibration during concrete finishing, and many vibrating systems have previously been proposed. Vibration during screeding helps "settle" the concrete, and helps to densify and compact the concrete during finishing. Vibrational screeding also removes air voids and brings excess water and fine layers of cement aggregate to the surface for subsequent finishing and, in general, promotes the attainment of a uniform product. Often screeds are adapted to extend between and rest upon the forms between which the plastic concrete is actually confined. Forms constrain the concrete until it is set, and provide a working support for the typical screen or finishing machine.
A prior art self-propelled "triangular truss" screed of the form riding type is shown in my prior U.S. Pat. No. 4,577,993. A winch-driven, self-propelled screed is also seen in my prior U.S. Pat. No. 4,363,618 and the various references cited and discussed therein. My prior U.S. Pat. Nos. 4,349,328 and 4,316,715 are also germane to the general technology discussed herein. All of the above patents have been assigned to the same assignee as the present case.
Screeds capable of formless, self-supporting or floating operation are shown in U.S. Pat. Nos. 4,650,366 and 3,386,901. The latter reference discloses a relatively heavy triangular truss screed adapted to be employed by a pair of workmen without the use of forms. U.S. Pat. No. 4,650,366 discloses a light weight, portable vibrating screed including a central, extruded beam element. A floating screed manufactured by Les Placements Paro of Canada, although it is not necessarily prior art and it is apparently unpatented, is believed relevant. It includes a floating pan which is physically offset from, and adjustably coupled to, a parallel and spaced-apart strike-off knife assembly.
U.S. Pat. No. 3,431,336 discloses a vibrating finishing screed adapted for use upon plastic concrete which apparently is capable of floating. U.S. Pat. No. 2,314,985 discloses a vibratory hand screed including a central, vibrated pan which is apparently adapted for use upon plastic concrete without support upon confining forms.
Other prior art includes "bull floaters" which have long been used in the concrete finishing arts. Such devices essentially comprise a flat wooden board attached to a handle, much like a broom handle, which are adapted to be manipulated by a single worker. Another prior art floating screed of general relevance is disclosed in a video tape produced by the American Concrete Institute and The Portland Cement Association, entitled "Finishing Concrete Flatwork," which bears a Copyright date of 1984. Other prior art screeds, generally of the "form-riding" type, include those screeds disclosed in U.S. Pat. Nos. 4,340,351; 4,105,355; 2,651,980; 2,542,979; 3,095,789; 2,693,136; and 4,030,873.
However, none of the prior art devices known to me provide a satisfactorily efficient system for manually finishing plastic concrete with portable, formless, floating screeds which can be conveniently and concurrently used for vibrating, striking-off, and float finishing. I have discovered an important function in the combined strike-off and flotation screed finishing function, which resides in the relationship between the buoyancy of the pan, its resultant surface tension, and the overall center of gravity obtained by the apparatus, and I have endeavored to perfect a floating screed wherein the aforementioned factors are harmoniously balanced.